Well Stimulation.
Oil and gas well stimulation plays a vital role in production operations. With oil and gas prices at all-time highs in 2008, it is imperative from an oil or gas company's perspective and a consumer's perspective that as much production as possible be safely extracted from the subterranean reservoir.
Natural production tendencies for wells are for the oil or gas production rates, and reservoir pressure, to be at its highest at initial production, and fall-off considerably as the well is produced. Typically, oil rates decline as water production increases causing the permeability of the reservoir to decrease, thereby reducing flow of fluid to the perforations in the casing of the well bore, driving up operating costs while revenue shrinks. This scenario continues until the well fails and/or becomes uneconomic to operate or repair. Thus, the purpose of oil or gas well stimulation is to increase a well's productivity by restoring oil production to original rates less normal decline, or to boost production above normal predictions.
Stimulation operations can be focused solely on the wellbore or on the reservoir, it can be conducted on old wells and new wells alike; and it can be designed for remedial purposes or for enhanced production. There are two main types of stimulation operations, matrix acidization and hydraulic fracturing.
Matrix acidization involves the placement of acid within the wellbore at rates and pressures designed to attack an impediment to production without fracturing or damaging the reservoir. Typically, hydrofluoric acid is used for sandstone/silica-based problems, and hydrochloric acid or acetic acid is used for limestone/carbonate-based problems. Most matrix stimulation operations target up to a ten foot radius in the reservoir surrounding the wellbore.
Hydraulic fracturing, which includes acid fracturing, involves the injection of a variety of fluids and other materials into the well at rates that actually cause the cracking or fracturing of the reservoir formation. The variety of material includes, but is not limited to, water, acid, special polymer gels, and sand. The fracturing of the reservoir rock and the subsequent filling of the fractured voids with sand (“proppant”) or the creation of acid channels allows for an enhanced conduit to the wellbore from distances in excess of a hundred feet.
The following patents discuss methods and systems for stimulating oil or gas production from subterranean wells: U.S. Pat. No. 7,198,103 to Campbell, Method for Stimulating a Petroleum Well; U.S. Pat. No. 7,278,481 to Eken, Method and System for Producing an Oil and Gas Mixture through a Well; U.S. Pat. No. 7,360,595 to Zupanick et al., Method and System for Underground Treatment of Materials; U.S. Pat. No. 7,380,606 to Pursley et al., Composition and Process for Well Cleaning; U.S. Pat. No. 7,419,223 to Seams, System and Method for Enhancing Permeability of a subterranean Zone at a Horizontal Well Bore.
Collectively, the above references describe a variety of stimulants or well stimulation methods that are either oil based or use synthetic compositions injected into the well and recovered, when possible. Often the well stimulation additives and methods include the use of caustic, harsh acids, such as sulfuric acid, hydrofluoric acid, hydrochloric acid and the like or combustible or flammable liquids. The prior art stimulation additives are harmful to equipment, people who work in the industry, and create disposal hazards in the environment. Even more alarming are reports from landowners that hydraulic fracturing of oil and gas wells has allegedly contaminated underground drinking water because aquifers are known to exist in and around formations with fluid underground resources, such as, natural gas, oil and water.
There is a need for a well stimulation additive and method that is heat tolerant, not pressure sensitive, not harmful to the environment or health of human workers in the well drilling industry and, importantly, can be disposed of without detrimental environmental impact to animals, land or water. The present invention fulfills that need.
Stuck Drill Pipe
Another aspect of drilling oil and gas wells involves drilling through subterranean and geological formations wherein, specialized drilling fluids, referred to as “muds,” are used to help maintain well control and to remove drill cuttings from the hole. The drilling pipe or string can become stuck in the hole, causing catastrophic delays in drilling, significant loss of time and money. There are a number of causes which may contribute to the stuck drill pipe problem including hole cave-in, blow-outs, mud or filter cake buildup in the bore hole. It is essential to free the stuck drill pipe as quickly as possible, with the least amount of down time and the least amount of damage to equipment, the environment and the operators.
Historically, either water-based muds (WBMs) or oil-based muds (OBMs) have been used for offshore wells. Recently, in response to U.S. Environmental Protection Agency (EPA) regulations and drilling-waste discharge requirements imposed by North Sea nations, the drilling industry has developed several types of synthetic-based muds (SBMs) that combine the desirable operating qualities of OBMs with the lower toxicity and environmental impact qualities of WBMs.
Each drilling fluid has positive and negative features. For example, on the positive side, water-based muds (WBMs) do not release free oil, are usually without toxic contaminants such as cadmium and mercury, are typically discharged at the well site and are widely used in shallow wells and in shallower portions of deeper wells; however, on the negative side, in deep or extended-reach wells, the performance of WBMs is often poor. Thus, for deep well intervals and complex drilling situations, oil-based muds (OBMs) and synthetic-based muds (SBMs) are needed for their superior performance.
The problem with OBMs is that U.S. Environmental Protection Agency (EPA) guidelines prohibit release of free oil, as detected by the static sheen test, from drilling fluids and drill cuttings discharges. Thus, OBMs must be recycled and cannot be discharged on-site, so there is the added cost of hauling and disposing of wastes onshore and long-term liability concerns associated with onshore disposal sites. OBMs also pose greater risk to workers through skin irritation and the effects of inhalation. Thus, despite their unique and valuable properties widespread use of OBMs is severely limited.
With regard to synthetic-based muds (SMBs), the synthetic liquid forms the continuous phase, while brine serves as the dispersed phase. The synthetic based fluids are classified according to the molecular structure as, esters (synthesized from fatty acids and alcohols), ethers, usually synthesized from alcohols (U.S. Pat. No. 4,614,235 to Keener et al.), poly-alphaolefins (manufactured by the catalytic polymerization of linear alpha-olefins), olefin isomers (manufactured by selective isomerization of normal alpha-olefins) and other base compounds are reported.
An oil-based stuck pipe additive containing propoxylated C18-C32 alkanols, an oil-soluble emulsifier-wetting agent and if desired an imidazoline for high temperature emulsion stability is reported in U.S. Pat. No. 4,436,638 and U.S. Pat. No. 4,464,269 to Walker et al.
SBMs have a wide range of chemical properties, drilling performance and environmental impacts, advantages and disadvantages for drilling operations and disposal of cuttings. For example, SBMs have drilling and operational properties similar to OBM systems and are used where OBMs are commonly used in difficult drilling situations, such as, high downhole temperatures, hydratable shales or salt, where the properties of WMBs would limit performance. Experience has shown that SBMs have higher cost, superior drilling performance and lower environmental impact than OBMs. SBMs must be recycled, with only the cuttings and a small amount of associated drilling fluids being disposed of on-site, if EPA and other environmental regulations will permit. Since 1990, several low-toxicity, biodegradable SBMs have entered the market. However, restrictions on discharge of cuttings pose a barrier to their use.
U.S. Pat. No. 5,247,992 to Lockhart describes a fluid for releasing stuck drill pipe that contains one or more carboxylic acids with specific chemical and physical properties.
In U.S. Pat. No. 7,033,976 B2 to Guzman a fluid system additive for use in hydrocarbon exploitation used a biopolymer derived from at least one species of the banana family that allegedly reduces the costs and environmental effects of existing additives.
Nonetheless, a drilling mud or stuck pipe additive is still needed by the drilling industry that provides superior drilling performance, low environmental impact, no release of oil, reasonable cost, and no toxicity to man or the environment.
In addition, the drilling industry needs fluid compositions and methods for production operations and remedial operations of all kinds, throughout a well's life, including well stimulation to increase productivity. It is desirable that the fluid compositions and methods have low environmental impact, reasonable cost, little or no toxicity to man or the environment.
The present invention fulfills many of the needed attributes of a stuck pipe additive and provides a fluid system additive that supports and improves the efficiency of a water-based mud (WBM) system and a well stimulation system for the drilling industry.